1. Field of the Invention
The present invention relates to a fuel, and methods, for reducing harmful emissions, particularly engine-out smoke/PM levels, from engines of the direct injection compression ignition type, particularly diesel engines. The present invention also relates to methods of operating vehicle fleets, or providing fuel to vehicle fleets, to meet motor vehicle emissions regulations at a reduced cost.
2. Background of the Invention
The continuing use of diesel engines in motor vehicles greatly adds to the atmospheric presence of harmful pollutants such as nitrogen oxides (NOx) and particulate matter (PM). It is well-known that conventional diesel engines emit NOx and/or PM substantially in excess of acceptable environmental levels. For purposes of this invention, environmentally acceptable levels of diesel NOx emissions will be defined as 0.2 g/bhp-hr or lower, and environmentally acceptable levels of diesel PM emissions will be defined as 0.01 g/bhp-hr or lower, with or without exhaust aftertreatment.
Despite their harmful emissions, the use of diesel engines nevertheless provides significant advantages as well. For example, diesel engines are significantly more energy efficient than gasoline engines. Because of their fuel efficiency, resulting in lower operating fuel costs, diesel engines remain economically preferable to gasoline engines for many applications where fuel costs are important, such as with larger vehicles and vehicle fleets.
Attempts to reduce NOx and PM emissions from diesel engines, without sacrificing the fuel efficiency benefits of diesel engines or significantly increasing the cost of diesel engines or fuel, have therefore continued for many years, with much improvement still to be made.
To meet upcoming environmental regulations as to NOx and PM emissions for diesel engines, the diesel industry has turned primarily to development of NOx and PM aftertreatments (i.e. post-engine, but before the exhaust gas is released to the atmosphere) to keep emissions within environmentally acceptable levels. However, currently many in the diesel industry view such aftertreatment systems as expensive, as retaining issues of effectiveness and durability, and as creating size (“packaging”) concerns. Because of these perceived problems with the expense and performance of such aftertreatment systems, it is desirable to develop an alternative; namely, a commercially acceptable diesel combustion system and method that can meet environmentally acceptable levels of NOx emissions (i.e. 0.2 g/bhp-hr or lower) and PM emissions without the need for aftertreatment, or with reduced aftertreatment needs, to reduce costs.
The parent applications hereto, incorporated by reference above, set forth a commercially acceptable diesel combustion system that can meet environmentally acceptable levels of NOx emissions (i.e. 0.2 g/bhp-hr or lower) without NOx aftertreatment, and with PM levels that are manageable with current PM aftertreatment technology. Engines that operate in accordance this combustion system, and potentially alternative combustion systems with the same goal (i.e., in keeping peak combustion temperatures below significant NOx forming levels), shall be referred to herein collectively as “Controlled Temperature Combustion” engines.
Even with these advances, it remains desirable to bring about continuing reductions in engine-out PM emissions (i.e. before aftertreatment) in Controlled Temperature Combustion engines, to further reduce PM aftertreatment costs. For example, further reduction of engine-out PM emissions may allow foregoing the use of a PM trap altogether with such engines, or use of a less expensive PM trap, or allow less frequent trap regeneration, as the frequency of required trap regeneration in diesel engines is dependent upon the engine-out PM emission levels.
Meanwhile, given the volatile and/or rising costs of fuel for internal combustion engines worldwide, it would also be desirable to reduce the cost of fuel for use with Controlled Temperature Combustion engines, just as with any internal combustion engine. One method of reducing the cost of fuel for Controlled Temperature Combustion direct injection compression ignition engines would be to enable use of less demanded fuels and fuels within a wider range of fuel specifications for such engines, which would increase the percentage of crude oil that can economically be made into fuel for such engines, beyond that which is typically used for making conventional diesel fuel. For example, providing a fuel that is suitable for use with Controlled Temperature Combustion direct injection compression ignition engines, from cuts or blends of fuel that previously would not be suitable for use in direct injection compression ignition engines and which are in less demand, may reduce fuel costs for such engines.